Stabilized magnetron circuits



Dec. 16, 1947. p GLASS 2,432,748

STABILIZED MAGNETRON CIRCUITS Filed Jan. 4, 1944 2 Sheets-Sheet l I FIELD STRENGT E I PAUL GLASS w, m 1:KIM/am Patented Dec. 16, 1947 2,432,748 STABILIZED MAGNETRON CIRCUITS Paul Glass, Chicago, Ill.,

Regulator Company,

assignor to Askania a corporation of Illinois Application January 4, 1944, Serial No. 516,995

9 Claims. (Cl. 179-171) This invention relates to stabilized control circuits employing electron tubes of the magnetron type.

An object of the invention is to devise a control or translating circuit employing an electron relay of the magnetron type and wherein the output current or voltage varies substantially in proportion to the input current or voltage.

A further object is to devise a translating circuit employing an electron relay of the magnetron type for producing a substantially linear indication of mechanical movements.

Still another object is to devise a circuit employing magnetrons for repeating or translating signal currents of either polarity and in which the output current has a linear relation with the input current.

According to my invention I provide a biasing magnetic field normally adjusted to a value sufficient to reduce the current in the anode circuit substantially below the maximum value. An input means is provided to cause a change in the value of anode current, either by modifying the biasing field or by varying the spacial relations between the electrodes of the magnetron, and a balancing winding provided on the magnetron is energized in proportion to the change in value of the anode current and in a direction tending to restore the original value of the anode current. The action of the balancing magnetizing winding serves to produce a substantially linear relation between the input signal and the anode current.

Examples of my invention are illustrated in the accompanying drawin in which Figure 1 is a diagrammatic representation of one form of translating circuit;

Figure 1a shows a characteristic curve for a magnetron type of electron tube;

Figure 2 shows a modification of the circuit of Figure 1 and also using a modified tube construction;

Figure 3 shows a modification of the circuit adapted for the indication of the extent of movement of an element;

Figure 4 shows an arrangement in which the anode of the magnetron is movable for indicating the extent of movement of a moving element;

Figure 4a is an end view of the tube employed in Figure 4;

Figure 5 is a circuit employing two magnetrons connected in back to back relation;

Figure 5a shows two curves for explaining the operation of Figure 5;

Figure 6 shows a modification of Figure 5; and

Figure 6a shows a curve for explaining the operation of Figure 6.

Referring to the drawing, the magnetron tube is diagrammatically represented in Figure l as involving a glass envelope l shown in dotted lines containing a cylindrical anode 2 and a heated cathode 3 arranged along the axis of the anode. The cathode 3 is heated from any suitable supply circuit including a source of current to and a variable resistance 3?). The anode 2 is maintained at a positive potential with respect to the cathode by source 4 which is included in the anode circuit in series with a resistance 5 and a current measuring instrument 6. A biasing or magnetizing winding 1 surr0unds envelope I and is energized from a suitable source 1a through an ad- J'ustable resistance 1b. This coil establishes a magnetic flux within the annular space between the cathode 3 and the anode 2 and having a direction parallel with theaxis of the anode and cathode. A second coil 8 surrounds the tube and is connected to be energized from input terminals 8a and 81) by suitable signals to be reproduced or indicated. A third magnetizing winding 9 surrounds the tube and is connected to be energized from the anode circuit of the magnetron. In the present case, the winding 9 is connected across a variable portion of resistance 5 by means of a slider contact So, although the winding 9 could be connected directly in series with the anode circuit and be provided with a variable shunting resistance. While windings I, 8 and 9 are shown in the drawing as being located on difierent sections of tube I, this showing is for convenience only. The preferred arrangement is one in which windings I, 8 and 9 are arranged in concentric relation and each winding extends substantially throughout the length of the tube, but other arrangements are possible.

In Figure 1a is shown the characteristic curve of a magnetron, that is, the curve shows the manner in which the anode current varies with the strength of the magnetic field established in the annular space surrounding the cathode 3. As shown" in the curve, the magnetic field has very little influence on the value of the anode current until the field reaches a value represented by the line F, and any increase in field strength beyond the value F results in a very rapid decrease in the anode current until it is finally reduced to zero or cut-off when the field strength reaches a value F. It is well known that the magnetic field within the annular space surrounding the cathode causes the electrons proceeding from the cathode to travel in curved paths about the axis of the cathode, the curvature of the paths increasing with the field strength. With high values of field strength in excess of value F, the paths are so curved that the electrons do not reach the anode and no current flows in the anode circuit. If the field strength is less than value F, some of the electron paths will extend out to the anode and current will flow in the anode circuit depending upon the number of paths intersected by the anode. When the field strength is less than the value F, practically all of the electrons emitted by the cathode are intercepted by the anode.

In the operation of Figure 1 according to my invention, the current in biasing winding 1 is adjusted until the field strength is at the cut-off value F as shown in Figure 1a and no current flows in the anode circuit. The signal to be measured is supplied to input winding 8 in a direction to oppose the magnetizing action by winding 1, and this will cause current to flow in the anode circuit and through resistance 5. Current will also flow through magnetizing winding 9 which is connected in shunt to a variable portion of resistance and in a direction to oppose the magnetizing action of the input winding 8. The current in the anode circuit will increase until the magnetizing action of balancing winding 9 is almost, but not quite, equal to the magnetizing action of input winding 8. The anode current increases until a state of equilibrium is established, and the value of the current flowing through meter 6 will provide an amplified indication of the signal current supplied to coil 8. The potential drop across resistance 5 will also be substantially proportional to the value of the signal current, and this potential may be employed for energizing or controlling a load circuit connected to terminals 5b.

In Figure 2 I have shown a somewhat different arrangement of the electrode elements of the magnetron. In this arrangement, the cathode 3 instead of being a rod-like element is formed in the shape of a helix, and the anode 2 is formed as a rod-like element positioned along the axis of the cathode helix. Also, instead of employing a separate balancing winding 9, a variable portion of the potential drop across resistance 5 is introduced in series with input winding 8 and in a direction to oppose the signal current applied to terminals 8a8b. The biasing winding I is provided for the same purpose as in Figure l, the current in this winding being normally adjusted so that the tube operates at the cut-off point F.

When a signal is applied to the input terminals 8a--8b of Figure 2 the current flowing through coil 8 tends to reduce the field strength and thereby permits the current to fiow in the anode circuit which establishes a counterbalancing voltage in the input circuit by reason of the potential drop across a portion of resistance 5 which is included in the input circuit. The anode current increases until a state of equilibrium is reached. The anode current indicated by meter 8, and the voltage across load circuit 51), will be substantially directly proportional to the value of the applied signal.

It will be understood that the balancing winding 9 may be omitted in Figure 1 and the winding 8 may be connected in the same manner as in Figure 2 if desired.

In Figure 3 I have illustrated a different method of obtaining the biasing field for the magnetron. Instead of applying the biasing winding 1 directly to the tube, this winding is applied to a magnetic structure l0 which has two pole pieces extending over opposite ends of the tube. For measuring electric signals, the remainder of Figure 3 is the same as Figure 1 and the signals would be applied to input terminals 8a8b. In this case, the magnetic core l0 could be a solid element.

In order to adapt the structure of Figure 3 for the measurement of variable movements, an air gap 10a is provided in the magnetic element l0, and a movable magnetic element Nib is arranged to act as a bridge over the gap Illa, the bridge element HJb being connected for movement by any suitable means through a connecting rod lllb. It will be understood that the movement to be measured or indicated shifts bridge element lob and thereby changes the amount of bridging of the gap Illa.

Operation of Figure 3 for the purpose of measuring or indicating movement is as follows. With the bridge 18b in its zero or normal position, current in winding 1 is adjusted until the field strength is at the cut-off point F in Figure 1a. The movement to be measured is then applied to move the bridge in a direction to increase the reluctance of the bridge to gap which decreases the strength of the magnetic field and permits current to flow in the anode circuit and through balancing winding 9. The action of winding 9 tends to restore the field strength and to reduce the anode current. The action is such that for a given movement of the bridging element Hlb, a predetermined current will flow in the anode circuit and will be indicated by the meter 6, or a predetermined value of voltage will be applied to the load circuit 5b from across resistance 5.

By providing means for oscillating bridging element lfib with respect to gap Illa, the arrangement of Figure 3 may be employed as an oscillation generator.

Where Figure 3 is to be used for repeating or indicating electric signals, the biasing coil 1 may be dispensed with provided the magnetic structure i8 includes a permanent magnet to supply the biasing field, the value of which may be adjusted by the bridging member Hlb.

In Figure 4 I have shown a magnetron circuit for measuring or indicating mechanical movements. In this arrangement, the cathode 3 is mounted in fixed position concentric with the anode 2 which is supported on a rod 2a extending through a flexible diaphragm Ia which forms a portion of the tube envelope I. An end view of the tube is shown in Figure 4a. The biasing winding 1 is provided for supplying the normal biasing field as in Figure 1, and the counterbalancing winding 9 is also arranged as in Figure 1 to supply a magnetizing force in the same direction as winding 1.

Operation of Figure 4 is as follows. The normal biasing field supplied by winding 1 is adjusted to the cut-ofi point F in Figure 1a with the anode 2 in its normal position where cathode 3 is located at the center of the anode. If now the upper end of rod 2a is moved in the direction of the arrow in Figure 4a, by some means not shown, the rod will pivot about its point of support (diaphragm la) and the concentric relation of the anode and cathode will be disturbed, that is, the right side of the anode will approach closer to the cathode and will thus intersect some of the circular paths of travel of the electrons from the cathode and current will be established in the anode circuit. The current which flows in balancing winding 9 will be in a direction to increase the magnetic field within the anode and will therefore tend to reduce or limit the value of the anode current. The amount of current which fiows through meter 6, or the voltage appearing across terminals 51), will be substantially proportional to the amount of movement of the anode supporting rod 2a. It will be understood that movement of the rod 2a in either direction from its normal position will result in the same action within the magnetron.

In Figure 5 I have shown a circuit in which two magnetrons are connected in back to back or push-pull relation for the purpose of measuring, indicating or otherwise translating signal impulses of either polarity. In this arrangement two magnetrons I and I have their cathodes connected to the negative terminal of source 4 and their anode circuits are completed through resistances 5 and 5 respectively. Magnetron I is provided with windings I, 8 and 9 arranged as in Figure 1, and magnetron I is provided with a similar set of windings I, 8' and 9. A resistance 5" is connected across resistances 5 and 5" in series with meter 6, and the output terminals 512 are connected across resistance5. The two balancing windings 9 and 9' are connected in series across a variable portion of resistance 5". The biasing windings I and I are connected in series with source Ia and rheostat 1?). These two windings are provided with variable shunt resistances as shown for the purpose of varying the relative values of current flowing through the two coils. Input windings 8 and 8' are also connected in series between input terminals 8a and 8b. The various windings are connected to produce magnetomotive-force in the relative directions indicated by the arrows.

Operation of Figure 5 is as follows. The normal biasing fields of the two magnetrons I and I are adjusted so that no potential difference appears across load terminals 5b when no signal is applied to the input terminals. This condition will be satisfied when the two magnetrons are operating according to Figure 5a. In this figure the vertical line I is the vertical axis for the characteristic curve A of magnetron I while the line ll-I is the vertical axis for the characteristic curve A of magnetron I. It will be assumed that instead of representing anode current values,

curves A and A across resistances represent the potential drops and 5', which potential drops will be proportional to the anode currents. By adjusting the currents in windings I and 1' so that the potential drop across resistance 5 is equal to the potential drop across resistance 5, then no difference of potential will exist across output terminals 51). With such an adjustment, the normal operating point for the two tubes is represented by the point B in Figure 5 where the two curves A and A cross each other.

Assume now that a signal is applied to the input terminals with the terminal 8a being positive; input winding 8 will increase the field strength in magnetron I while winding 8' will decrease the field strength in magnetron This means that the anode current in magnetron I will decrease while the anode current in magnetron I will increase. The resulting potential drop across resistance 5 will decrease, for example, from the point B to the point C in Figure 5a and the potential drop across resistance will increase from the point B to the point C. A difference of potential will now appear across output terminals 51) equal to the difierence between the values of the points C and C. It will be understood that the balancing windings 9 and 9 operate to limit the amount of change in the anode currents in the same manner as described above in connection with Figure 1.

Where the input signal causes terminal 811 to be positive, the operation will be the same as described above except that the point C inFigure 5 will rise above the point B, while the point C falls below the point B, and the potential appearing across the output terminals will be reversed in polarity.

The arrangement shown in Figure 6 is the same as that shown in Figure 5 except that windings I, 8' and 9' are reversed in connection so that the direction of the field set up in each coil is reversed from that of Figure 5.

The operation of Figure 6 will be understood from Figure 5. If it is assumed that magnetrons I and I have the same characteristic, then thetwo curves for the two magnetrons will be superimposed and may be represented by a single curve shown in Figure 6a. The biasing currents in the two magnetrons are adjusted so that both magnetrons operate normally at the point B with no signal applied to the input terminals. When a positive signal is applied to terminal 8a, the signal current increases the value of the field in magnetron I and decreases the field in magnetron I, thus shifting the operating point for magnetron I down to the point C, and shifting the operating point for magnetron I up to the point C. The resulting difference in potential drop across resistances 5 and 5 will be the diifera ence in values of the points C and C which will be indicated by the voltmeter 6a and will appear across output terminals 511.

It will be obvious to those skilled in the art that the details of my invention may be varied in various ways without departing from the principle of the invention. One obvious modification of Figures 5 and 6 would be the omission of balancing windings 9 and 9 and the connections to these windings could be inserted in series with the input circuit at the point 8c in the same manner as in Figure 2.

I claim:

1. A translating system comprising, in combination, an electron tube having a cathode and an anode, one of said electrodes being arranged concentric with the other to provide an annular space therebetween, an output circuit including a source of current connected between said cathode and said anode, means for establishing within said annular space a magnetic field whose lines of force are substantially parallel to the cathode whereby the electrons are caused to travel in curved paths in said annular space, input means for varying the number of electrons received by said anode to vary the current flowing in said output circuit, and means energized from said output circuit to vary the number of electrons received by said anode in an opposite direction with respect to the variation produced by said input means.

2. A translating system according to claim 1 wherein said input means comprises means for varying the strength of said magnetic field.

3. A translating system according to claim 1 wherein said input means comprises means for changing the spacing between the anode and cathode.

4. A translating system comprising, in combination, a magnetron tube including a pair of concentric electrodes comprising an anode and a cathode, an output circuit including a source of current connected between said electrodes, means for establishing a magnetic field in the annular space between said electrodes, said field being of sufficient strength to cause the electrons emitted by the cathode to travel in curved paths which do not intersect the anode, input means for changing the relation between the electron paths and said anode so that some of said paths are intersected by said anode and current is established in said output circuit, and means energized in proportion to the value of said current for increasing the strength of said magnetic field.

5. A translating system according to claim 4 wherein said input means comprises means for decreasing the strength of said magnetic field.

6. A translating system according t claim 4 wherein said input means comprises means for shifting one of said electrodes into eccentric relation with respect to the other.

7. A translating system comprising, in combination, a magnetron tube, including a pair of concentric electrodes comprising an anode and a cathode, an output circuit including a source of current connected between said cathode and said anode, means for establishing a biasing magnetic field in the annular space between said electrodes to cause said magnetron to normally operate on a steeply sloping portion of its characteristic curve, input means for controlling said magnetron to shift the point of operation on the characteristic curve, and means energized from said output cricuit for modifying said biasing field in a direction tending to oppose said shift in operating point.

8. A translating system comprising, in combination, a pair of magnetron tubes each including a pair of concentric electrodes comprisin an anode and a cathode with means for establishing a magnetic field in the annular space between said electrodes, a source of current having its negative terminal connected to the cathodes of said magnetrons, a connection from each anode of said magnetrons to the positive terminal of said source each including a coupling impedance, an output circuit connected around said coupling impedances, means for adjusting the magnetic fields of said magnetrons so that normally each magnetron operates on a steeply sloping portion of its characteristic curve and no difierence of potential appears across said output circuit, an input circuit including means for varying the magnetic fields of said magnetrons in opposite directions, and means energized from said output circuit and tending to vary the magnetic fields of said magnetrons in a direction opposite to the change caused by said input circuit.

9. A translating system comprising, in combination, a pair of magnetron tubes each including a pair of concentric electrodes comprising an anode and a cathode with means for establishing a magnetic field in the annular space between said electrodes, an output circuit, a source of current having its negative terminal connected to the cathodes of said magnetrons, separate connections from the positive terminal of said source to the anodes of said magnetrons, said anode connections being coupled to said output circuit in push-pull relation, means for adjusting the magnetic fields of said magnetrons so that normally each magnetron operates on a steeply sloping portion of its characteristic curve and substantially equal currents flow in said tubes, an input circuit including means for varying the magnetic fields of said magnetrons in opposite directions, and means energized from said output circuit and tending to vary the magnetic fields of said magnetrons in a direction opposite to the change caused by said input circuit.

PAUL GLASS.

REFERENCES CITED The following references are of record in the file of this patent: 

